Cryogenic apparatus support structure



April 12, 1966 CANTY ETAL 3,245,571

CRYOGENIC APPARATUS SUPPORT STRUCTURE Original Filed Aug. 25, 1961 2 Sheets-Sheet l A T TORNEV April 12, 1966 J. M. CANTY ET AL 3,245,571

CRYOGENIC APPARATUS SUPPORT STRUCTURE Original Filed Aug. 25, 1961 2 Sheets-Sheet 2 INVENTORS JOHN M. CANTY VINCENT E. FIRST RICHARD J. FRAINIER ODD A. HANSEN ATTORNE United States Patent Ofiice 3,245,571 Patented Apr. 12, 1966 3,245,571 CRYOGENIC APPARATUS SUPPORT STRUCTURE John M. Canty, Vincent E. First, and Richard J. Frainier,

Tonawanda, and Odd A. Hansen, Kenmore, N.Y., assignors to Union Carbide Corporation, a corporation of New York Continuation of application Ser. No. 134,069, Aug. 25, 1961. This application Feb. 18, 1964, Ser. No. 346,587

" 13 Claims. (Cl. 220 B) This application is a continuation of copending application Serial No. 134,069, filed August 25, 1961, now abandoned.

This invention relates to cryogenic apparatus and particularly' to support structures for supportably separating thermally isolated objects.

Cryogenic apparatus support structures are frequently required to separate objects having temperatures which differ on the order of 400 to 550 F. In such applications, it is imperative that, whatever the load carrying requirement-s, these support structures not provide an unrestricted thermal path for the conduction of heat from the warmer to the colder object. An inherent problem, for example, in the design of present day double-walled, thermally insulated containers for cryogenic liquids is that of adequately supporting the inner product liquid vessel within the surrounding outer protective shell and, at the same time, maintain the leakage of ambient heat into the inner vessel at a reasonably low level.

It is'not uncommon to find that the heat leak path provided by typical prior art inner vessel support structures contributes a substantial proportion of the total heat inleakage to the inner vessel, such as 30 to 50 percent. By adhering to reasonably careful design techniques in combination with the employment of relatively high quality thermal insulating systems, the heat inleakage through the insulating system may be reduced. However, it is much more difficult to appreciably reduce the heat inleakage through the inner vessel support structure. A relatively high percentagecontribution to the total heat inleakage, such as 30 to 50 percent, may be tolerable in such-applications as the storage of liquid oxygen and nitrogen. Where the storage of such cryogenic liquids as liquid hydrogen and liquid helium are concerned, however, such a large percentage contribution to the total heat inleakage may well be intolerable. Preferably, in such service, the heat leak path provided by the inner vessel support structure should contribute less than about 30 percent of the total heat inleakage, which is oftentimes very diificult to achieve when loss of the valuable product liquid because of excessive evaporation caused by heat'inleakage must be kept below, for example, about 1 percent of container capacity per day. Simply increasing the length of the support structure or employing materials having a lower thermal conductivity may not suffioe. Such procedures may cause difficult design and fabrication problems, in addition to considerably increasing the costs of fabrication.

The principal object of this invention is to provide a support structure for separating thermally isolated objects such that the heat inleakage therethrough is less than prior art support structures, and yet adequately provide structural support for such objects. Another object is to provide a support structure for resisting dyscription thereof together with the accompanying drawing which is a view in longitudinal crosssection of a support structure embodying the principles of the present invention.

The support structure of this invention comprises a tension rod and multiple disk structure combination for separating thermally isolated objects, such as the inner vessel of a double-walled, thermally-insulated cryogenic liquid storage container. The multiple disk structure is preferably slightly preloaded to assure adequate dimensional stability of the disks and control of the supported objects. This support structure is most useful for resisting dynamic forces, such as those frequently experienced by mobile storage containers having an inner vessel suspended from the container outer shell, wherein the multiple disk structure is relatively highly compressed for only a small portion of the time.

It is well known to use low thermally-conductive metal rods to suspend thermally insulated objects, such as the inner vessel of double-walled, vacuum-insulated containers for cryogenic liquids. While such tension rods are useful for unidirectional support of small or nearly spherical shaped inner vessels in which a minimum number of tension rods may be required, they do not adequately sufiice for longer cylindrical vessels, where differential contraction or expansion of the outer shell relative to the inner vessel may be appreciable, and where the inner vessel must withstand substantial dynamic forces experienced in all directions. Under these conditions, several tension rods are usually required, which increases the heat transfer into the inner vessel to an undesirable degree. One prior art method of reducing the heat transfer through such tension rod support structures is to use tension rods designed to withstand two-directional forces, i.e., both tensile and compression forces. However, designing solid or hollow rods to withstand compressive forces in addition to tensile forces may also result in excessive total heat transfer through the support structure.

The present invention solves this support problem by combining with a tension rod, a multiple disk structure which is dynamically compressible, but only whenever a force is experienced in a direction opposite to the direc tion of those forces absorbed by the tension rod. Heat transfer by conduction through this multiple disk structure or stacked disks as it will hereinafter be called, when it is relatively unstressed, is quite small and increases only slightly when compressed. Thus, relatively appreciable heat transfer through the stacked disks occurs only during the time when they are dynamically compressed.

The disks may be of any shape such as rectangular, hexagonal, or generally annular, but the preferred shape is circular. The cross-section of the disks may be fiat, or contoured, such as, for example, a chevron cross-section. Such disks may be constructed as a continuous, longitudinally-oriented helix or, as is preferable, as individual members. Depending on the load carrying requirements, the disks may be constructed of thin stainless steel, Micarta, or very thin glass sheets; stainless steel being preferable for resisting large dynamic forces. If it is desired to thermally separate the individual layers of the multiple disk structure, for example when it is constructed as a continuous, longitudinally-oriented helix, such structure could be dipped in a solution of some low thermally conductive material such as an inorganic silicate. Of course, other methods and materials could be used to accomplish such a thermal separation.

Although the tension rods may be made of any high strength, low thermally conductive material, the preferred tension rod material is Hastelloy B alloy which is an austenitic-type alloy having the following composition:

The preferred material for the stacked disks is stainless steel sheet between about 0.0005 in. and about 0.010 in. thick, and preferably about .002 in. thick. Employment of thinner disks results in more contact surfaces per unit length of stacked disks, and thus provides for lower thermal conductivity.

As the stacked metal disks are progressively compressed, the rate of deflection per unit load is initially quite high, but decreases rapidly as the unit load increases above about 3,000 p.s.i. Also, as the stacked disks are progressively compressed, the thermal conductivity initially increases rapidly after which the rate of increase is lower and substantially constant. Thus, it has been found that a relationship exists between the deflection and the thermal conductivity of the stacked disks such that after a useful compressive force resulting in a stress of about 3,000 p.s.i. is applied, further increases in unit compression load cause only moderate corresponding increases in deflection and thermal conductivity. Thus, it is contemplated that this invention will be employed in applications where the stacked disks are pre-compressed to above 3,000 psi. In any application, however, some degree of prel-oading of the stacked disks is desired to provide adequate structural control of the members being supported.

Among the important uses of this tension rod and stacked disk support structure is an inner vessel support structure for vacuum-insulated containers. The thermal conductivity through the stacked disks is influenced by the surrounding gas pressure, the apparent thermal conductivity through the tension rod and stacked disk combinations being greater at ambient pressure than in a vacuum. Thus, the preferred use of this support structure is expected to be in applications where the total heat leakage must be maintained at a relatively low level, such as that achieved by vacuum insulations.

The support structure of this invention, as it is employed to resist forces experienced alternately in opposite directions, may be oriented in any manner as desired. For example, this support structure may be employed to resist vertically and horizontally applied forces in supporting an inner vessel within the outer shell of a doublewalled vacuum-insulated container.

FIG. 1 depicts generally the essential features of the tension rod-stacked disk support structure of the present invention. Inner wall is separated from outer wall 12 by space 14 which is preferably evacuated and substantially completely filled with opacified insulating material 16. Tension rod 18 may be attached to inner wall 10 through reentrant tube 20 by any suitable means,

such as by being threadably engaged therein as shown,

and may be attached to outer wall 12 by, for example, threaded nut 22, the latter connection being preferably covered by a pressure tight cap 24. FIG. 2 depicts a double-walled Vacuum-insulated container employing the tension rod-stacked disk support structures at opposite ends of the container. Although four such structures have been illustrated, in practice the selected number is 4 based on the particular support requirements of the inner container 10. This container ma'y' for example be-used to store liquid oxygen, introduced through top conduit 29 having valve 30 therein and withdrawn through bottom conduit 3'1 and valve 32.

The term opacified insulation as used herein refers to a two component insulating system comprising a low heat conductive radiation permeable material and a radiant heat impervious material which is capable of reducing the passage of infrared rays without significantly increasing the thermal conductivity of the insulating system.

As more fully described and claimed in copend-ing US. application Serial No.-597,947, filed July 16, 1956, in the name of L. C. Matsch, and issued November 7, 1961, as US. Patent 3,007,596, the low heat conductive material may be fibrous insulation which may be produced in sheet form. Examples of such a material include a filamentary glass material such as glass wool and fiber glass, preferably having fiber diameter less than about 50 microns. Also such fibrous materials preferably have a fiber orientation substantially perpendicular to the direction of heat fiow across the insulation space. The spaced radiation-impervious barriers may comprise either a metal, metal oxide, or metal coated material, such as aluminum coated plastic film or other radiation reflective or radiation adsorptive material or a suitable combination thereof. Radiation reflective material comprising thin metal foils are preferably suited in the practice of the present invention. For example, reflective sheets of aluminum foil having a thickness between 0.2 mm. and 0.002 mm. may be employed when fiber sheets are used as the low-conductive material, they may additionally serve as a support means for the relatively fragile radiation-impervious sheets. For example, it may be preferred that an aluminum foil-fiber sheet insulation be spirally wrapped around inner wall 10 with one end of the insulation wrapping in contact with inner wall 19 and the other end nearest outer wall 12 or in actual contact therewith.

It will be appreciated that other forms of opacified insulation may be used. For example, the radiation impervious barriers may be incorporated directly into the low heat conductive material as described and claimed in Us. Patent No. 2,967,452 issued inthe name of L.- C. Matsch et al. Such opacified powder-vacuum type insulation might comprise, for example, equal parts by weight of copper flakes and finely divided silica. The latter material has a very low solid conductivity value but is quite transparent to radiation. The copper flakes serve to markedly reduce the radiant heat inleak.

Even though the previously described preferred opacified insulation is more effective than straight vacuum insulation at higher internal pressure (poorer vacuum), its effective thermal insulation life is extended if the pressure can be maintained at'or below a desired level such as, for example, below about microns of mercury absolute. A gas removing material such as an adsorbent may be used in insulation space 14 to remove by adsorption any gas entering through the joints of the inner and outer walls. In particular, crystalline zeolitic molecular sieves having pores of at least about 5 angstrom units in size, as disclosed in US. Patent No. 2,900,800 issued in the name of P. E. Loveday, may be employed as the adsorbent in accordance with the teachings therein since this material has extremely high adsorptive capacity at the temperature and pressure conditions existing in insulation space 14 and is chemically inert toward any gases which might leak into such insulation space. The adsorbent material may be provided within insulation space 14, for example, by iutermixing the same with the insulation or by placing it in a blister (not shown) such that a screen provides gas communication between the blister and the insulation space/ Intermediate to walls and 12, .a plurality of thin, stacked metal disks 25 of any desired shape are located concentrically around tension rod 18 as shown. These disks are preferably aligned by, and retained on, cylindrical tube 26, which may be constructed of thin, low thermally-conductive metal or a thermo-setting plastic. It is essential to this invention that, howsoever stacked disks 25 are retained, tension rod 18 must be capable of independent movement relative to stacked disks 25. In order to further minimize the conduction of ambient heat through tension rod '18, the same will probably be greater in length than the cumulative length of stacked disks 25.

This unique combination of stacked disks and a tension rod permits suspending an inner vessel solely by the tension rods while employing the stacked disks to absorb upward dynamic compressive forces without compressing such tension rods. The stacked disks are slightly compressible and act somewhat like a spring and thus tend to reduce dynamic forces as opposed to a solid metal compression support. Also, the stacked disk support is shorter .and more stable than a solid compression support having equivalent heat transmitting characteristics. In the preferred embodiment, tension rod 18 is supported through threaded nut 22 by outer wall support 28. Stacked disks 25 are pre-compressed to above about 3,000 p.s.i. by tightening threaded nut 22 on tension rod '18. Any upward force which might be experienced by the container, for example such as might be created by shocks due to bumps which a moving container would undergo, is sub stantially completely absorbed by stacked disks 25.

A preferred manner of assuring that tension rod 18 will not absorb compressive forces is to permit tension rod '18 and threaded nut 22 to move relative to outer wall support 28. Consequently, tension rod 18 need only be designed to withstand tensile forces thereby permitting a smaller diameter thereof and a resulting restricted heat leak path therethrough.

While the stacked disks may be guided on either their external or internal surfaces, they are preferably guided on the internal surfaces by a separate thin tube. Use of a separate guide means such as tube 26 to align and guide the stacked disks, instead of the tension rod itself, allows the stacked disks and tension rod to be proportioned independently as desired. For example, when using threaded ends on the tension rod, for reason of uniform strength, the outside diameter of such threaded ends will usually be greater than the diameter of the tension rod as shown by the figure, thus preventing the stacked disks from being slipped onto the tension rod unless they are of larger inside diameter. However, if the load rod is, for example, hollow and does not have enlarged threaded ends, it could also serve as a guide for the disks.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

What is claimed is:

1. A structure for supporting two thermally isolated objects in spaced relationship to each other comprising a tension rod fixedly attached to one of said objects and slidably attached to the other object and positioned between the two objects such that said tension rod maintains said spaced relationship only against forces which impose longitudinal tensile forces on said tension rod and moves relative to said other object when subjected to longitudinal compressive forces; and a multiple disk structure positioned between said objects concentrically with and independently of said tension rod, said multiple disk structure maintaining said spaced relationship against dynamic forces which impose on said multiple disk structure compressive forces in a direction opposite to the direction of the tensile forces imposed on said tension rod.

2. A structure according to claim 1 wherein said multiple disk structure comp-rises a plurality of stainless steel disks each between about 0.0005 to 0.010 inch thick.

3. A structure according to claim 2 wherein said stacked disks are pre-compressed to at least about 3,000 psi.

4. A structure for supporting two thermally isolated objects in spaced relationship to each other comprising a tension rod fixedly attached to one of said objects and slidably attached to the other object such that said tension rod maintains said spaced relationship only against forces which impose longitudinal tensile forces on said tension rod and moves relative to said other object when subjected to longitudinal compressive forces; a multiple disk structure positioned between said objects concentrically with and independently of said tension rod, said multiple disk structure maintaining said spaced relationship against dynamic forces in a direction opposite to the direction of the tensile forces imposed on said tension rod; one thermally isolated object comprising a cryogenic liquid storage inner vessel and the other thermally isolated object comprising an outer protective shell spaced from and surrounding the inner vessel thereby defining an insulation space therebetween, said inner vessel being suspended from the outer shell by said structure.

5. A structure according to claim 4 wherein said tension rod is connected to said outer shell such that said tension rod is longitudinally movable relative to said outer shell and is connected to said inner vessel; and including means for concentrically positioning said multiple disk structure around said tension rod.

6. A structure according to claim 4 wherein the space between and defined by the thermally isolated objects is evacuated to a pressure below about microns of mercury.

7. A structure according to claim 6 wherein said space is substantially completely filled with opacified insulation.

8. A structure according to claim 1 wherein the crosssection of said multiple disk structure is contoured.

9. A structure according to claim 1 wherein said multiple disk structure comprises a continuous, longitudinallyoriented helix.

10. A structure according to claim 9 wherein the crosssection of said multiple disk structure is contoured in the shape of a chevron.

11. A structure according to claim 9 wherein individual surfaces comprises such helix and are thermally separated.

12. A structure according to claim 1 wherein the crosssection of said multiple disk structure is contoured in the shape of a chevron.

13. A structure according to claim 1 wherein individual surfaces comprises such helix and are thermally separated.

References Cited by the Examiner UNITED STATES PATENTS 2,417,715 3/1947 Stewart 267-1 2,708,110 5/1955 Clay 267--1 3,004,683 10/1961 Bushhold 220l5 3,016,160 1/1962 Scharpf 220l5 3,102,655 9/1963 Adkins et al 220l5 LOUIS G. MANCENE, Primary Examiner.

THERON E. CONDON, Examiner. 

4. A STRUCTURE FOR SUPPORTING TWO THERMALLY ISOLATED OBJECTS IN SPACED RELATIONSHIP TO EACH OTHER COMPRISING A TENSION ROD FIXEDLY ATTACHED TO ONE OF SAID OBJECTS AND SLIDABLY ATTACHED TO THE OTHER OBJECT SUCH THAT SAID TENSION ROD MAINTAINS SAID SPACED RELATIONSHIP ONLY AGAINST FORCES WHICH IMPOSE LONGITUDINAL TENSILE FORCES ON SAID TENSION ROD AND MOVES RELATIVE TO SAID OTHER OBJECT WHEN SUB- 